This invention relates to a racket frame, and particularly to a looped head of the racket with two symmetrically opposite inner peripheral indentations with respect to the longitudinal axis of the looped frame.
A conventional looped racket frame generally has an outer grooved peripheral face extending along the length of the looped head and a substantially convexed opposite inner peripheral face, wherein the string lines of the racket run to and fro passing through the string holes from the inner peripheral face to the outer grooved peripheral face which provides a channel to guide the string to turn inward. The looped frame is generally oval-shaped which has a longitudinal axis and a transverse axis.
Generally, the direction of a ball stroke by a racket depends of the characteristics of the string web and the point on the string web where the ball strikes. The angle of deflection of individual string lines relative to the plane of the string web formed upon striking the ball is one of the important characteristics of the string web. The deflection angles of the string lines are not identical since the lengths of the string lines are different depending on their positions in the looped frame. FIGS. 1 to 5 show the deflection angles of different string lines when a ball strikes at P1, P2, P3 and P4 on the string web.
When the ball impacts at the point P1, the center of symmetry of the looped frame, the ball will generally be rebounded in a direction perpendicular to the string web without deviation. This point is the best point that permits the player to best predict the direction of the ball. When the ball impacts points other than the point P1, the directions of the rebound becomes difficult to predict. This is because the the striking points bisect both the longitudinal and transverse strings into segments of unequal length and thus will cause different deflection angles of the strings with respect to the string web. The different deflections of the two string portions on two sides of the point cause the rebound ball to uncontrollably deflect from the vertical line with respect to the string web.
Referring to FIGS. 2 and 3 in combination with FIG. 1, the impact points P2 and P3 are on different longitudinal lines AA and BB but on the same transverse line CC. The line BB is longer than the line AA and thus the line BP3 is longer than the line AP2. Therefore, the deflection angle .theta.2' of the longer line BP3 is smaller than the angle .theta.1' of the shorter line AP2. As a result, the deflection angle .theta.2 of the ball rebounded from the longer string BB is smaller than the angle .theta.1 of the ball rebounded from the shorter string AA. Similarly, FIGS. 4 and 5 shows different angles of deflection of the balls occurring at points P2 and P4 on a shorter transverse lines CC and a longer transverse line DD.
In view of the above facts, a general conclusion can be made such that the longer in the string line is the smaller in the deflection angle of the ball. As a matter of fact, the direction of a ball is not merely affected by a deflected single line but by several deflected string lines including longitudinal and transverse lines. Therefore, the direction of the ball depends on the total effect of the strings impacted by the ball, which renders the direction of the ball difficult to predict. In order to easily control the ball, it is desirable to minimize the deflection angles of the ball imparted by the string web. To this end, it is necessary to lengthen the strings.